Ion transport and energy conservation in submitochondrial particles

Abstract

The combination of valinomycin and nigericin in the presence of K⁺ uncouples submitochondrial particles (SMP) as evidenced by: 1) loss and release of the oligomycin-induced respiratory control; 2) inhibition of the P/0 ratio; 3) inhibition of three energy-linked reactions — pyridine-nucleotide transhydrogenation, reversal of electron-transfer, and bromthymol blue and 8-anilino-1-naphtalenesulfonate responses; and 4) change of redox state of cytochromes to the same extent obtained with conventional uncouplers. Neither antibiotic alone, in the presence of K⁺, markedly affected the energized state of the system. Direct measurements of K⁺ and H⁺ movements showed that SMP did indeed translocate these ions in a predictable manner, i. e., a nigericin-stimulated influx of K⁺ to SMP, followed by a valinomycin-mediated efflux of the K⁺ taken up. The NH ₄ ⁺ -dependent uncoupling is demonstrated to be associated with the uptake of NH ₄ ⁺ by SMP with a consequent collapse of the pH gradient established during respiration, followed by a valinomycin-mediated efflux of the NH ₄ ⁺ taken up. The effects of cations and antibiotics can be mimicked by suitable combinations of cations and anions, suggesting that the valinomycin-mediated efflux of cations from SMP is electrophoretic in nature and can be replaced by an electrophoretic influx of appropriate anions. Analogies are drawn with observations reported on bacterial chromatophores and chloroplasts, and a general scheme is suggested. The implications of these results are discussed in terms of the current hypotheses of energy coupling in oxidative and photosynthetic phosphorylation.